1. Field of the Invention
This invention relates to field emission electron sources characterized by low-turn-on voltages, low gate-to-source current leakage, and low anode-to-gate or source current leakage. The field emission sources of the present invention have applicability to flat-panel displays using cathodoluminescent phosphors, CRT's, electron beam tubes, and other free electron devices.
2. Description of the Related Art
In the technology of field emission structures and devices, a microelectronic emission element, or a plurality (array) of such elements, is employed to emit a flux of electrons from the surface of the emission element(s). The emitter surface ("tip") is specifically shaped to facilitate effective emission of electrons, and emitted electron beams are directed, e.g., with the assistance of focusing electrodes or other directionally orienting structures, to an anode, which may comprise a plate member bearing an array of phosphors or other electroluminescent elements, to provide a selected visual output.
Field emission display devices may be fabricated in a wide variety of shapes and sizes, and much effort has been directed in recent years to the development of field emission-based flat panel displays, for computer, graphic, and telecommunications applications.
In the fabrication and use of such field emission devices, leakage current and flashover directly affect the cost of electronic components required for flat-panel video displays. These operational phenomena also affect the energy efficiency and performance of the field emission devices.
Tomii et al. U.S. Pat. No. 5,053,673 teaches the formation of vertical field emission structures by forming elongate parallel layers of cathode material on a substrate, followed by attachment of a second substrate so that the cathode material layers are sandwiched therebetween in a block matrix. Alternatively, the cathode material layer can be encased in a layer of electrically insulative material sandwiched in such type of block matrix. The block then is sectioned to form elements having exposed cathode material on at least one face thereof. In the embodiment wherein the cathode material is encased in an insulative material, the sliced members may be processed so that the cathode material protrudes above the insulator casing. The exposed cathode material in either embodiment then is shaped into emitter tips (microtip cathodes).
Spindt et al. U.S. Pat. No. 3,665,241 describes vertical field emission cathode/field ionizer structures in which "needle-like" elements such as conical or pyramidal tips are formed on a (typically conductive or semiconductive) substrate. Above this tip array, a foraminous electrode member, such as a screen or mesh, is arranged with its openings vertically aligned with associated tip elements. In one embodiment disclosed in the patent, the needle-like elements comprise a cylindrical lower pedestal section and an upper conical extremity, wherein the pedestal section has a higher resistivity than either the foraminous electrode or the upper conical extremity, and an insulator may be arranged between the conical tip electrodes and the foraminous electrode member. The structures of this patent may be formed by metal deposition through a foraminous member (which may be left in place as a counterelectrode, or replaced with another foraminous member) to yield a regular array of metal points.
Copending U.S. application Ser. No. 08/029,880 filed Mar. 11, 1993 in the name of Gary W. Jones discloses a vertical field emitter structure and field emission device such as a flat panel display utilizing such structure. Self-aligned gate and emitter fabrication are described, together with virtual column field emitter structures, comprising an emitter or gated emitter with conductive columns connecting the emitter to an underlying resistor or conductor structure formed by chemical or other modification of portions of an underlying layer. The display disclosed in this copending application utilizes field emission structures with low turn-voltages and high accelerating voltages, thereby permitting high brightness, small pixel size, low manufacturing costs, uniform brightness, and high energy efficiency to be achieved.
Copending U.S. application Ser. No. 08/290,238 filed Aug. 15, 1994 in the name of Gary W. Jones discloses an imaging apparatus for providing an image from a display to an observer, including a display generating an optical output, an imaging surface member constructed and arranged for viewing by an observer, and a scanning mirror/lens assembly optically interposed between the display and the imaging surface member, and constructed and arranged to motively repetitively scan the display, generate a scanned image, and transmit the scanned image to the imaging surface member, for viewing of the scanned image. Various field emitter display designs and subassemblies are described in this copending application, which may be usefully employed in the imaging apparatus.
In field emitter technology, as exemplified by the structures and devices described in the above-discussed patents, there is a continuing search for improvements, particularly under the impetus of commercial as well as military interest in the development of practical and reliable flat panel display devices.
More specifically, in the provision of commercially acceptable flat panel video displays based on field emission devices, leakage current and flashover considerations directly affect the cost of electronic components of the display, and affect the energy efficiency and performance of the devices.
It would be a substantial advantage in the art, and is an object of the present invention, to provide a field emission electron sources characterized by low turn-on voltages, low gate-to-source current leakage, and low anode-to-gate or source current leakage.
It is another object of the present invention to provide a field emission source of such type having applicability to flat-panel displays using cathodoluminescent phosphors, CRT's, electron beam tubes, and other free electron devices.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.